Magnetoresistive memory devices store information with stable magnetic states that result in different device resistances. For example, in certain magnetoresistive memory devices, the resistance across a magnetic tunnel junction (MTJ), and therefore the voltage drop for a specific current, depends on the relative magnetic states of the magnetic layers within the memory cell. In such memory devices, there is typically a portion of the memory cell that has a “reference” magnetic state and another portion that has a “free” magnetic state that is controlled to be either parallel or antiparallel to the reference magnetic state. Because the resistance through the memory cell changes based on whether the magnetic vector for the free portion is parallel or antiparallel to the magnetic vector for the reference portion, information can be stored by setting the magnetic orientation of the free portion. The information is later retrieved by sensing the orientation of the free portion. Such magnetic memory devices are well known in the art. As described herein, the free portion may be referred to as a “free layer” and the reference portion may be referred to as a “reference layer” even though each of the free and reference portions may be made up of many layers of both ferromagnetic and non-ferromagnetic materials.
While magnetoresistive memory devices provide non-volatile storage under many operating conditions, there is a need for more robust data storage in such devices such that the data is maintained even after the memory is exposed to adverse conditions, including the heat associated with soldering operations and/or packaging.